SOFTENING EFFECTS ON THE SEISMIC RESPONSE OF NON-DUCTILE CONCRETE FRAMES

An approach for predicting the response of non-ductile reinforced concrete (RC) frames subjected to seismic loading is proposed. A beam-column element is developed based on component tests. The main characteristic of the developed element is its ability to represent the drop in the strength of non-ductile RC members after reaching the ultimate strength level. The term softening is used to define the reduction in the component strength capacity under cyclic loading after reaching the ultimate strength limit. Moment and deformation capacities of the frame members are estimated. The analytical predictions are compared with experimental measurements of the response of members of non-ductile frames. The approach is applied to study the seismic response of a three-storey non-ductile frame. The response calculated using the softening model is compared with the prediction using traditional models that do not represent the strength softening of the frame members. It is concluded that ignoring the strength softening underestimates the deformation as members of the frames pass their ultimate strength.